1. Field of the Invention
The present invention relates to a rotary hinge shaft assembly, and particularly to such a rotary shaft assembly which has a stationary shaft part engaging a movable shaft part with a tight fit, to simplify and to reduce the assembly time. In addition, an oil groove is provided on the movable shaft to provide sound lubrication such that noise can be avoided.
2. Description of Related Art
Usually, consumer electronic products having a lid such as a portable computer, an electronic dictionary, a portable video-audio playing device, etc. have a lower main body with an upper lid. A rotary hinge shaft links the main body and the lid such that the lid can open and close effectively. Hence, the rotary shaft is one of factors to determine if the above said products are good or not. In fact, an excellent rotary shaft is one which does not become loose under repeated operations. It is necessary also for the rotary shaft to be prevented from generating noise so as to avoid the user having an uncomfortable feeling.
Generally, there are two kinds of ways that friction is generated on a rotation shaft and one of the friction ways is series type, i.e., the axial friction, of which an example has been disclosed in U.S. Pat. No. 5,190,391 (the identical invention was granted as Taiwanese Utility Model No. 73784). Because the present invention is not related to the series type of friction, no further detail will be described. The other of the friction ways is sleeve type, i.e., the radial friction, of which an example has been disclosed in U.S. Pat. No. 5,632,066 (the identical invention was granted as Taiwanese Utility Model No. 111911). In order to acquire an expectant stagnating effect of location, the conventional sleeve type of rotary shaft has to meet a strict requirement of precision. That is, the male connecting member and the female connecting member of the rotary shaft is made of metal being easily ground and cut. In this way, an axial hole can be formed in the female connecting member and a split groove can be formed on a cylinder part at the center of the male connecting member. Then, the cylinder part can be flexibly inserted into the axial hole. After grinding and cutting, the male connecting member and the female connecting member have to be heat-treated so as to increase the strength and durability thereof. However, the cylinder part frequently is distorted through the heat treatment caused by the cylindrical hole. Therefore, it is not possible to properly fit with the axial hole.